Recently, information technology has been frequently utilized in various business fields. As a business is carried forward, various pieces of data involving the business are generated and most of the data so generated is retained for recording of the details of the business concerned and for later utilization.
For example, in a medical system, a retention period for which data on each patient such as images indicative of a result of inspection performed on the patient, a text indicative of a result of medical examination performed on the patient and information on medicines prescribed to the patient is to be retained is provided by law. Thus, in the medical system, long-term retention of mass data is indispensable.
As media for retaining data, a hard disk, a magnetic tape, a semiconductor memory and the like may be given. In many cases, a magnetic tape which is relatively low in cost per storage capacity is used to retain mass data.
However, since the magnetic tape is of a sequential access type, it is not suited to retain data frequent and random access to which is necessary.
In a medical system of the above mentioned type, data is stored every time each medical examination is finished and the stored data is read out every time the next medical examination is to be performed. Therefore, random access to the data concerned is required and long-term retention of the mass data which has been generated consequently is also required.
In order to meet the above mentioned requirements, such a system is proposed that it includes a magnetic tape and a hard disk so as to store mass data in the magnetic tape and to store data which is high in access frequency in the randomly accessible hard disk, thereby attaining both mass data storage and random accessibility.
In a system of the above mentioned type that long-term retention of data is indispensable, it may sometimes occur that in the case that the amount of stored data is increased and residual storage capacity of a storage medium for storing data is decreased accordingly or in the case that the service life of an ever used system has expired, the ever used system has to be replaced with a new system.
In replacing the ever used system with the new system, it is necessary to move data stored in the ever used system to the new system. In the above mentioned situation, a magnetic tape is highly stably used to store data even when the data is to be retained for a long time period and, in addition, a magnetic tape is a matured medium standard of which is hardly updated, so that the possibility that it will be used as it is also in the future is high. Therefore, movement of data stored in the magnetic tape is possible simply by moving the magnetic tape used in the ever used system to the new system as it is.
On the other hand, the possibility that a hard disk will fail is increased with increasing its use time. Therefore, it is desirable to move data stored in the hard disk to the new system by reading data out of the hard disk in the ever used system and storing the data then in a new hard disk installed in the new system.
However, a technique for moving data to a new system by storing the data then in a new medium has such a problem that data movement takes much time. The time required for data movement is proportional to the data amount. In the case that mass data has to be moved as in the case in a medical system as described above, in some cases, for example, several days to several months may be took.